The present invention relates to a bending press for bending metal sheet, the press being of the type comprising a top panel placed above a bottom panel, the bottom panel being fixed and supported at its ends while the top panel is movable and actuated in a vertical plane by drive members likewise situated at its two ends.
The drive members deliver the force required for bending metal sheets or laminations and these give rise to oppositely-directed deformation of the two panels.
With that type of structure, under the action of the bending forces, the longitudinal deformation curves of the panels (each curve being in the form of a single arc) are substantially symmetrical about the separation plane of the panels such that the maximum separation between the panels occurs in the vicinity of the midpoint between the thrust points (drive members and fixed supports) and represents twice the maximum deformation of each panel.
The maximum separation between the top and bottom panels is an essential parameter concerning the precision and the quality of the bending performed, and in the above-mentioned case, since the two panels are separated to a greater extent in the middle than at the ends, the bending will be more open in the center than at the ends.
To mitigate that drawback, a solution is proposed in Japanese utility model No. 2 558 928 which describes a bending press comprising a moving top panel and a fixed bottom panel constituted by a plate of uniform thickness having two notches made therein that are symmetrically identical about the transverse midplane of said bottom panel.
Each notch has a top wall and a bottom wall that are interconnected by a back wall and also has an opening situated in the corresponding side edge of the plate.
The plate thus has a bottom portion and a top portion situated respectively below and above the notches. Advantageously, the bottom portion of the plate is fixed to two cheek plates that also support the top panel, while the top portion of the plate, or more exactly its ends, are free to move in a vertical plane.
Under such conditions, under the action of bending forces, longitudinal deformation curves are obtained for the two working edges of the top and bottom panels that are as parallel as possible, and therefore as close together as possible.
That Japanese utility model also states that each of the notches is provided with a moving member whose position can be adjusted manually or automatically within the notches. The moving member comes directly into contact with the bottom and top walls of each notch and moving the moving member makes it possible to reduce the equivalent depth of said notches, thereby reducing the elasticity of the bottom panel as the moving member is moved closer to the open ends.
Unfortunately, the use of that type of bending press does not make it possible to ensure that the deformation curves of the facing edges of the bottom and top panels are accurately parallel.
The pressure exerted on the free top portion of the bottom panel is a function only of the force applied by the work of the drive members on the top panel, and consequently by the sheet metal to be folded, and nothing in those conditions makes it possible to take voluntary action on said pressures and thus on the deformation to which said top portion of the bottom panel is subjected in order to cause it to deform accurately parallel to the deformation to which the top panel is subjected.
Furthermore, when the moving member lies substantially level with the back wall of the notch and the force applied by the work of the members is large, the deformation curve of the bottom panel is then at its maximum, in which case the intrinsic elasticity of the top portion of the bottom panel can be irremediably harmed.
An object of the present invention is to overcome the above-mentioned technical problems in satisfactory manner.
The invention achieves this object by means of a bending press for bending sheet metal, the press being of the type comprising a top panel disposed above a bottom panel, the bottom panel being fixed and supported at its ends while the top panel is moving and actuated in a vertical plane by drive members situated likewise at its ends, the bottom panel being constituted by a plate having a free top portion and a fixed bottom portion defined by two notches that are symmetrically identical to the transverse midplane of said bottom panel, each notch having a top wall and a bottom wall interconnected by a back wall, and also having an opening situated in the corresponding side edge of the plate, the press being characterized in that each notch is fitted with a displacement member interconnecting the free top portion and the fixed bottom portion of the bottom panel so as to cause the top wall of the notch to move towards the bottom wall thereof, thereby modifying the deformation curve of the free top portion of said bottom panel in controlled manner.
According to another feature, each displacement member comprises firstly a fixed portion connected to the bottom wall of the notch and secondly a moving portion secured to the top wall of the notch.
According to another feature, each displacement member is situated in the opening of its notch, so as to enable the free ends of the top walls of said notches to be moved accurately.
According to another feature, the bending press includes a control unit for independently controlling each displacement member as a function of the curve to be given to each end of the free top portion of the bottom panel.
According to another feature which is advantageous, the control unit comprises:
means for receiving curve information concerning the curve to be given to the free top portion of the bottom panel; and
means for converting said curve information into control information for the displacement members.
According to yet another feature which is advantageous, the control unit further comprises measurement means for obtaining information about the actual curve of free top portion of the bottom panel, and the programmed curve.
Thus, the displacement member of the invention makes it possible to monitor and adjust in reliable manner the deformation curve of the free top proton of the bottom panel, and to do so without running the risk of exceeding the elastic limit of said bottom panel.
Furthermore, given that the deformation curve of the bottom panel is no longer a function of the force applied by the work of the drive members on the top panel, it will be understood that merely by performing strength and structure calculations concerning the top panel and the sheet metal to be bent, the displacement member can be adjusted accurately so that the extent to which the top wall of the notch moves towards the bottom wall is adjusted accurately, thereby making it possible to obtain deformation curves for the bottom and top panels that are accurately parallel.